Extraction of tetravalent plutonium values from aqueous acid solutions by 2 (beta-ethylbutoxy) ethanol



United States Patent i 2,996,526 EXTRACTION OF TETRAVALENT ,PLUTONIUM VALUES FROM AQUEOUS ACID SOLUTIONS BY 2(B-ETHYLBUTOXY)ETHANOL Glenn T. Seaborg, Chicago, 'Ill., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Original applicationlVIay 1, 1945, Ser. No. 591,410. Divided and this application Oct. 8, 1945, Ser. No. 621,182

4 Claims. '(Cl. 260-4291) The present invention relates to 'the solvent extraction of heavy metal compounds, and particularly to the extraction of a compound of a transuranic element from an aqueous solution thereof by means f an 'organic solvent.

An object of this invention is to provide .a'method for the separation of a transuranic element from aqueous solutions thereof.

Another object of this invention is toprovidexamethod for the separation and purification of a transuranic element contained in aqueous :solutions of :sai'delement and other elements of lower atomic weights.

A further object of the present invention'is to provide suitable organic solvents and extraction procedures for the separation of element .94 from aqueous solutions thereof. 7 I

Other objects and advantages of this inventionwillbe evident from the following description.

The term element 94 is used in this specification to designate the element of atomic number :94, which is also referred to herein as plutonium, :symbol .Pu. It has recently become known that various isotopes of element 94 can be prepared by a number ofzidiiierentnuclear processes. Thus, the plutonium visotope of mass 238, referred to as 94 can be prepared by deuteron bombardment of the uranium isotope 92 to :produce 93 followed by beta decay of the 93 to 94 3. 1('I11e.isotops 93 is the mass 238 isotope of the element :of atomic number 93, referred to as neptunium, symbol Np.) The plutonium isotopes 94 and 94 can be prepared by neutron bombardment of the uranium isotope -.of :mass 238:

Neutronic reactors for the production .of :element 94 .from natural uranium .by .a, self sustaining chain reaction have recently been developed. One of the. isotopes occurring in natural uranium .is 92 whichis .usually present to the extent of about 0.71% by weight. When this isotope is bombarded .by slow neutrons, preferably of thermal energies, it undergoes .fissionand releases on an average of about at least two neutrons per fission in addition to fission fragments of relatively low atomic weights. The isotopes 94 and 94 can also undergo fission when bombarded by neutrons, and theseffission processes also release on an average of about atleast two neutrons per neutron absorbed in the fission reaction. 'Thus, in a natural uranium neutronic reactor, the excess neutrons released by fission are .suflicient 'to maintain production of element 94 through neutron absorption by the predominant uranium isotope 92 .The concentration of plutonium so produced is generally small, rarelybeing above one percent by weight of the uranium and is usually substantially below such concentration.

Element 94 may suitably be separated from masses of uranium which have undergoneneutronbombardment for periods of time sufficient to produce recoverable amounts of plutonium, but which maybe insufiicient to :destroy more'than a minute fraction of the total uranium Patented Aug. 15, 1961 through fission of 92 and neutron absorption by 92 It may be desired to recover the plutonium content of such uranium masses having plutonium concentrations below 1 part per thousand and even below 1 part per million parts of uranium.

Neutron-bombarded uranium, or a neutron-bombarded uranium compound, will contain, in addition to plutonium and unreacted uranium, various radioactive fission products in a total concentration of the same order of magnitude as the plutonium concentration. The original fragments produced by fission are highly unstable radioactive isotopes of short half-lives which rapidly decay to longer lived isotopes. The fission products which are present after practicable aging periods will usually range in atomic numbers from about 32 to about 64 and in atomic masses from about 77 to about 158. These fission products comprise largely a light group in which isotopes of Sr, Y, Zr, Cb, and Ru are the most dangerously radioactive, and a heavy group in which isotopes of Te, I, Cs, Ba, La, Ce, and Pr are the most dangerously radioactive.

In the recovery of plutonium from neutron-bombarded uranium, the plutonium is conveniently processed in aqueous solutions, and preferably in aqueous inorganic acid solutions. Thus, in the initial separation of plutonium from the bulk of the unreacted uranium and fission products, in the further decontamination of the plutonium by separation from residual radioactive fission products, and in the final concentration, purification, and recovery of plutonium, it is desirable to effect the plutonium separations (from aqueous nitr'icacid or other suitable aqueous medium. Various precipitation methods have been suggested for the separation of plutonium from such aqueous .solutions. These methods, however, have generally entailed the use of large amounts of auxiliary carrier precipitates, and the .handling of very large vol- .umes of solutions.

In accordance with the present invention, plutonium compounds may be separated from aqueous nitric acid solutions, aqueous "hydrochloric acid solutions, or other suitable aqueous media, by extraction into organic solvents of the class hereinafter described. This solvent extraction procedure may be employed for the separation'of plutonium from aqueous solutions in any phase of the above-mentioned procedure for the recovery of plutonium from neutron-irradiated uranium. In addition, the'solvent extraction procedure of the present invention may be aqueous solution which forms ionic complexes with plutonium more strongly than does the nitrate ion. The hydroxyl ion, and the anions of acids whichionize in aqueous solutions to a substantially smaller degree than .nitric acid, are particularly disadvantageous from "the standpoint of complexing tetravalent plutonium. Thus, hydroxyl, sulfate, phosphate, fluoride, and oxalate "ions .tend to complex tetravalent plutonium suificiently .to decrease .its extractability into organic solvents. lt is there- .fore desirable to minimize the concentrations of freelions of this class in the aqueous solutions to be extracted.

Most of the complexing ions can be excluded in the preparation of the aqueous solutions. Alternatively, an interfering ion may itself be complexed by another ion, or its concentration asafree ion may otherwise be minimized by control of the concentration of another ion which can combine with it. Thus, the fluoride ion can be complexed by zirconyl ion, and the hydroxyl ion can be suppressed by hydrogen ion, to reduce their interference with the extraction of tetravalent plutonium. The extraction hexavalent plutonium is relatively free from interference by hydroxyl ion. Hexavalent plutonium can be extracted from aqueous solutions of any hydrogen ion concentration suflicient to prevent the precipitation of 'a basic plutonium compound. An aqueous solution of 'plutonyl nitrate may thus be extracted without the necessity of free nitric acid in the solution. In the case of tetravalent plutonium, on the other hand, it is desira- .ble to maintain free acidin the aqueous solution. Solutions of plutonous nitrate for extraction with organic solvents should have a pH not substantially above 2.5, and preferablyshould have a concentration of free nitric acid of at least 1 N. V if In order to improve the distribution of plutonium be- .tween the aqueous and organic phases, it is generally desirable to incorporate a salting-out agent in the aqueous solution. A salting-out agent, for this purpose, has the Same. characteristics as a salting-out agent for previously known solvent extraction processes, i.e., high solubility in the solution to be extracted and low solubility in the extract phase. The preferred salting-out agents for use jnthe present invention are thosehaving a common ion with respect to the compound being extracted. Thus,

7'" ""aaeepae if a nitrate of plutonium is being extracted, the saltingout agent is preferably an inorganic nitrate. Examples of suitable salting-out agents for this purpose are:

NaNO3 Sr z s g 3 )2 LiNO La(NO a NH NO Al(NO Theconcentration of the-salting-out agent which is desirable in any particular case will depend on the valence :of 'the cation and the concentration of 'the common anion due to any free acid in the solution. .In the case of 1 N nitric acid solutions, it is desirable to employ a concentration of a univalent nitrate of at least 3 M, and preferably 5-10 M. Equivalent concentrations of polyivalent nitrates may be employed at the same acid conicentrations, a'ndthe salt concentration may suitably be increased or decreased with decrease or increase in acid .concentration.

The extraction agents which are suitable for use in rmy process comprise normally liquid organic sol- :vents which are substantially immiscible with the aque- :ous solution to be extracted and which contain at least .xlv atom capable of donating an electron pair to. a co-" =solutions, and the oxygenated organic solvents are the tpreferred extractants for use in the present process.

Although most normally liquid organic compounds containing an atom with excess electrons, such as oxygen, sulphur, or nitrogen, are capable of forming a coordination bond, it will be evident to those skilled in the art that certain molecular structures can interfere with this electron-donating property. Electron attracting constitu- -en ts such as halogen atoms can off-set the electron-donat- =ing property of an atom such as oxygen, if present in 'suificient number andproper relationship to the donor atom. For this reason it is preferable to employ compounds containing only carbon, hydrogen, and electrondonor atoms. It will also be apparent that certain molecular configurations can give rise to steric hindrance which may interfere sufli'ciently to prevent the formatlon of coordination bo'nds. Tertiary carbon atoms adjacent an electron-donor atom and long chains of non-donor atoms linked to a donor atom are especially undesirable in this respect. The preferred solvents are those in which the donor atom 'is linked to a hydrogen atom or to nontertiary carbon atoms and in which at least one come ponent'linked to the donor'atom contains less than four consecutive non-donor atoms.

The following are exmaples of suitable solvents for use in-the present process: a

Ethyl'ether "17 .f 1' Z bis-fi-Chloroethyl ether 2-phenoxyethanol 2-benzyloxyethanol 1,2-diethoxyethane 1-ethoxy-2-butoxyethane 1,2-dibutoxyethane bis-fi-Butoxyethyl ether 1,2-bis-(fi-chloroethoxy) ethane 5,8,11,14,17-pentoxaheneicosane o-Nitroanisole 2,6-dimethyl-l ,4x-dioxane 1-oxa-2,5-dimethylcyclopentane Heptanol Heptadecanol' 2-ethylbutanol I :Methylisobutylcarbinol 'Methyl ethyl ketone Methyl amyl ketone Methyl isobutyl'ketone Mesityl oxide Acetophenone Cyclopentanone Cyclohexanone Menthone Isophorone Nitromethane W I Nitroethane Co l-nitropropane Nitrobenzene 7 Tributyl phosphate In employing any of the solvents of the above class in the present process, previously known extraction procedures and apparatus may be employed. The extraction 'may be eflected by batch, continuous batch, batch countercurrent, or continuous counter-current methods; The most efficient extraction is obtained in continuous countercurrent operation. The usual types of extraction equipment and. the usual operating procedures may be employed when eifecting the present extraction in this manner. Satisfactory extraction in accordance with this procedure may be obtained by the use of a packed column with aqueous feed atan intermediate point, solvent feed 'at the bottom of the column, and solvent draw-elf at the 'top of the column. The top section of such a column may serve as a stripping section, and a'n auxiliary stripping medium may optionally be charged to'the top of the column. R v ,H

I The plutoniummay be recovered from the solvent extract phase by any suitable procedure such as evaporation of the solvent, vcrystallization with an isomorphous crystalline carrier, re-extra'ction with another immisible solvent, or adsorption on a solid adsorbent.

. It is apparent that the procedures described above may be applied totheextraction ofplutoniumfrom solutions containing various impurities of lower atomicweig'ht "which are'insolublein the organic solvent employed.

asse seadvantageous in separating plutonium from the fission products contained in solutions derived from neutron irradiated uranium. This procedure is also useful in simultaneously extracting both plutonium and uranium from solutions of neutron bombarded uranium. Repeated extractions with one or more solvents may be used to eifect purification and concentration of plutonium to an extent sufficient to enable final recovery of a pure-compound of plutonium.

The present invention will be further illustrated with particular reference to certain preferred classes of solvents.

One preferred class of solvents for use in the present invention comprises ethers containing at least one oxygen atom capable of donating an electron pair to a coordination bond. The most desirable compounds of this class are the saturated aliphatic ethers, and it has been found preferable to employ an aliphaticether containing at least one. oxygen atom which is attached by an ether linkage to non tertiary aliphatic carbon atoms, at least one component' linked to said oxygen atom containing lessthan four consecutive non-donor atoms. The following examples illustrate the use of solvents of this. class:

Example 1 A solution of PuO in l M HNO -5 M Ca(NO was agitated in an equal volume of ethyl ether until the extraction equilibrium was obtained. The phases were then separated and the extract was analyzed for plutonium content on the basis of its alpha radiation and that of the original aqueous solution. The plutonium content of the extract was found to be 94% of that in the initial charge.

Example 2 Percent Extract 91.2 Rafiinate 8.3 Loss 0.5

Example 3 Uranyl nitrate hexahydrate, which had been subjected to neutron irradiation from 50 milliampers hours deuteron bombardment of beryllium and aged for 80 days, was melted, acidified with 70% nitric acid to 0.66 M HNO made 0.02 M in K Cr O with solid potassium dichromate, and held at 60 C. for about one hour to efiect oxidation of the plutonium to PuO The solution was then cooled to room temperature and extracted with approximately 5.3 times its volume of thyl ether, in a single stage batch extraction. The extract was found to contain 86% of the plutonium content of the aqueous charge, together with a substantially greater percentage of the uranium content of the charge, but only 8% of the fission products.

Example 4 A solution of PuO in 1 M HN0 --10 M NH NO was agitated with an equal volume of ethyl sulfide until the extraction equilibrium was attained. The phases were then separatedand the extract was analyzed for plutonium content on the basis of its alpha radiation and that of the original aqueous solution. The plutonium content of the extract was found to be 35% of that in the initial charge.

The substitution of normal propyl or isopropyl ethers for the ethyl ether in the. above examples will result in less advantageous distribution coefiicients, but adequate s extraction is obtainableinleflicienttcounter-current opera tion. l

The sulphur analogues. ofthe-ethers are also useful in this process, and the following example illustrates themeof a solvent of this type:

Example 5 A solution of PuO in-1 M HNOg-IO M NH NO was agitated with an equal volume of ethyl sulfide until the extraction equilibrium was attained. The phases were then separated and the extract was analyzed for. plutonium content on the basis of its alpha radiation and that of the original aqueous solution. The plutonium content of the extract was found to be 43% of that" in the-initial charge.

The glycol ethers comprise a preferredclassof solventshaving especially favorable distribution coefficients" for plutonium extraction. The desirable solvents of this class are saturated glycol ethers containing at least one oxygen atom which is attached by an ether linkage to a non tertiary aliphatic carbon atom, at least one component linked to said oxygen atom containing less than four consecutive non-donor atoms. The preferred ethers of this class are the monoglycol monoalkyl ethers, polyglycol monoalkyl ethers, monoglycol dialkyl ethers, and polyglycol dialkyl ethers. The following are examples of the use of solvents of this class:

Example 6 i A solution of Poof in 1. M HN'O --10 M.NH- NO was agitated with an equal volume of:1,2-diethoxyethane until extraction equilibrium. was. attained. The phases. were then separated and the extract: was. analyzed for plutonium content on the basis of its. alpharadiation and that of the original aqueous solution. The plutonium content of the extract was found to be 96% of that in the initial charge.

Example 7" Example 8' A solution of Pu in 0.6" M UO (.NO -l M HNO 10 M. NH NO was agitated with an equal volume of Z-(Bethylbutoxy) ethanol until the extraction equilibrium was attained. The phases" were then separataed and the distribution of plutonium and uranium between the aqueous and organic phases. was determined. The percentage extraction of each ofthe-metals from the initial aqueous solution was. found to be"- approximately as follows:

Percent Plutonium 60 Uranium 63 Example: 9

A solution of Pu' in 1. M HNO -IO. M NI-I N0 was agitated with an equal volume of. Z-benzyloxyethanol. After extractionequilibrium had been attained, the phases were separated and the extractv was analyzed for plutonium content. It was found that the extraction was approximately 48% complete.

Another preferred class of solvents for use in the present extraction process comprises normally liquid organic solvents containing at least one carbonyl oxygen. atom capable of donating an electron pair to a coordination bond. This class includes carbocylic acids, esters, aldehydes and ketones. The most desirable solvents of this group comprise aliphatic ketones and especially dialkyl ketones having a carbonylgroup attached to at least 1 non-tertiary carbon atom. The following are examples of the utilization of solvents of this cass in the present process:

' Example 10 Example 11 A solution of PuO;+ in water substantially saturated with lithium nitrate was agitated with an equal volume of organic solvent comprising 90% methyl ethyl ketone and 10% mixed xylenes. After extraction equilibrium had been attained, the phases were separated and the extract was "analyzed for plutonium content. It was found that the extraction was approximately 83% complete.

Example 12 A solution of Pu+ in 8 M HCl was agitated with an equal volume of methyl isobutyl ketone. After extraction equilibrium had been attained, the extract was analyzed for plutonium content. The extraction was found to be 91% complete.

Example 13 A lanthanum fluoride precipitate containing plutonous fluoride (Pu+ was dissolved in aqueous zirconyl nitrate and the resulting solution was made 3 M with respect to nitric acid and M with respect to ammonium nitrate. The concentrations of zirconium, lanthanum, and plutonium in this solution were approximately 18.6, 6.2, and 0.0001 g. per liter, respectively. The above solution was charged continuously to a packed extraction column at a point approximately 0.4 of the column length below the top of the column. Methyl isobutyl ketone was charged continuously to the bottom of the columnata rate approximately double the charge-rate of the plutonium solution, and an aqueous stripping solution, comprising 3 M'HNO --5 M NH NO was continuously chargedtto the top of the column at a rate approximately one-half the charge rate of the plutonium solution. The total charge to the column, per hour, was approximately 0.9 of the column hold-up.

After reaching equilibrium, the methyl isobutyl ketone extract, which was continuously withdrawn from the top of the column, and the spent aqueous solution, which was continuously withdrawn from the bottom of the column, were analyzed for plutonium content. The extract was found to contain approximately 99.75% of the plutonium in the charge solution, and the spent aqueous solution contained the residual 0.25%.

. Example 14 A solution of Pu+ in 1 M END M NH NO was agitated with an equal volume-of acetophenone until the extraction equilibrium was attained. The phases were then separated and the extract was analyzed for plutonium content on the basis of its alpha radiation and that of the original aqueous solution. The plutonium content of the extract was found to be 89% of that in the original charge.

Example 15 extraction equilibrium was attained. The phases were then separated and the extract was analyzed for plutonium content. The extraction was found to be approximately 47% complete. j V

A further class of preferred solvents for the present invention comprises normally liquid organic solvents containing at least one nitro oxygen atom capable of donating an electron pair to a coordination bond. Desirable solvents of this class comprise nitrohydrocarbons and especially nitroalkanes. The following are examples of the use of nitrohydrocarbons in the present process:

Example 16 A solution of Pu+ in 1 M HNO 10 M NH NO was agitated with an equal volume of nitromethane until the extraction equilibrium was attained. The phases were then separated and the extract was analyzed for plutonium content. The extraction was found to be approximately 58% complete.

Example 17 A solution of PuO in saturated aqueous lithium nitrate was agitated with 1.5 times its volume of nitromethane until the extraction equilibrium was attained. The phases were then separated, and the extract was found to contain approximately of the plutonium content of the original aqueous solution.

Example 18 A solution of PuO in 1 M HNO 10 M NH NO was agitated with an equal volume of nitroethane until the extraction equilibrium was attained. The phases were then separated and the extract was analyzed for plutonium content. The extraction was found to be approximately 61% complete.

Example 19 A solution of PuO in saturated aqueous lithium nitrate was agitated with 1.5 times its volume of l-nitropropane until the extraction equilibrium was attained. The phases were then separated, and the extract was found to contain approximately 81% of the plutonium content of the original aqueous solution.

Example 20 A solution of PuO in 1 M HNO 10 M NH NO, was agitatedzwith an equalvolume of nitrobenzene. The phases were then separated. and the extract .was analyzed for plutonium. content. The. extractionwas found to be approximately 28% complete.

It is to be understood, of course, that the above examples are merely'illustrative and do not limit the scope of my invention. Other solvents of the class previously described may be substituted for the specific solvents of these examples, and the procedures employed may be modified in numerous respects within the scope of the foregoing description. In general it may be said that the use of any equivalents or modifications of procedure which would naturally occur to those skilled in the art is included in the scope of my invention. Only such limitations should be imposed on the scope of this invention as are indicated in the appended claims. z

This is a division of co-pending application U.S. Serial No. 591,410, filed May 1, 1945, which is a continuationin-part of co-pending application U.S. Serial No. 481,660, filed April 3, 1943, and granted on October 29, 1957, as U. S. Patent No. 2,811,415, and all subject matter therein not inconsistent with the subject matter herein is incorporated by reference.

What is claimed is:

1. A process for the separation of tetravalent plutonium from an aqueous inorganic acid solution containing tetravalent plutonium ions and a common ion salting-out agent which comprises contacting said solution with 2-(fi-ethylbutoxy) ethanol, and separating the resulting extract and raflinate phases. a

2. The process of claim 1 in whichthe acidity of the Q plutonium-containing solution ranges between 1 N and a pH of 2.5.

3. A process of separating tetravalent plutonium values from an aqueous nitric acid solution also containing a water-soluble nitrate as a salting-out agent, comprising contacting said solution with Z-(B-ethylbutyoxy)ethanol whereby the tetravalent plutonium values are taken up by said 2-(B-ethylbut0xy)ethanol, and separating the 2- (B-ethylbutoxy)ethanol from the aqueous solution.

4. The process of claim 3 in which the acidity of the 10 plutonium-containing solution ranges between 1 N and a pH of 2.5

10 References Cited in the file of this patent UNITED STATES PATENTS 2,227,833 Hixson et al. Jan. 7, 1941 2,811,415 Seaborg Oct. 29, 1957 2,864,664 Spence et al. Dec. 16, 195-8 OTHER REFERENCES Maxwell: AECD-2134, pp. 1-4, Oct. 6,. 1944, de classified July 19, 1948, ABC, Oak Ridge, Tenn.

McMillan et al.: Physical Review, vol. 57, pp. 1185-6 (1940).

(SE L) UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No. 2 996 526 i August 15 1961 Glenn Ta Seaborg I It is hereby certified that error eppears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5 line 65 for PuO read P I line o for ffsu'lfidefi read =-'ether column 6 line EL for P110 read Pu O T" =0 Signed and sealed this ioth day of April 1962,

Attest:

ERNEST W. swIDER I I 7 I DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A PROCESS FOR THE SEPARATION OF TETRAVALENT PLUTONIUM FROM AN AQUEOUS INORGANIC ACID SOLUTION CONTAINING TETRAVALENT PLUTONIUM IONS AND A COMMON ION SALTING-OUT AGENT WHICH COMPRISES CONTACTING SAID SOLUTION WITH 2-(B-ETHYLBUTOXY)ETHANOL, AND SEPARATING THE RESULTING EXTRACT AND RAFFINATE PHASES. 